Calculating average utilization of the wireless link in PTP 670/700

Sometimes operators find it useful to know the utilization of a wireless link, meaning the percentage of the link capacity that is presently being used for network traffic. Results need to be treated with some caution, because in a network that uses TCP for reliable delivery and flow control, the wireless link may routinely saturate. That's simply a characteristic of TCP, and a higher capacity link would saturate just the same.

Anyway, having said that, some people would still like to know the utilization. We can calculate that using some SNMP objects introduced in 670-01-46, 670-02-60 and 700-02-60. We need to consider that for utilization to be sensible, we need an average over a period; sampling an instantaneous number is likely to give an unreliable indication. If you configure a management system to read wirelessOutEthernetOctets and wirelessOutAllOctets periodically, you can calculate as follows:

delta-wireless-out-ethernet-octets = wireless-out-ethernet-octets[n] - wireless-out-ethernet-octets[n-1]
delta-time = time[n] - time[n-1]
transmit-data-throughput = delta-wireless-out-ethernet-octets / delta-time.

transmit-data-throughput-mbps = 8 * transmit-data-throughput

For utilization, calculate:

delta-wireless-out-octets = wireless-out-octets[n] - wireless-out-octets[n-1]
delta-wireless-out-all-octets = wireless-out-all-octets[n] - wireless-out-all-octets[n-1]
utilization-percentage = 100 * delta-wireless-out-octets / delta-wireless-out-all-octets

This approach is particulary useful, because the result is a percentage of capacity; as modulation mode adapts, the capacity increases or decreases. The calculation here is based on the actual capacity available during the measurement period between sample (n-1) and sample n.

1 Like